The invention relates to an actuation circuit for an inverter for the operation of an electric drive motor of a vehicle, specifically of a road vehicle.
A vehicle with an electric drive system comprises a first energy store for the storage of electrical energy for the operation of an electric drive motor of the vehicle. The first energy store delivers a current at a relatively high first voltage (e.g. 300-400 V). Moreover, the vehicle typically comprises an on-board system, which operates at a relatively low second voltage (e.g. 12-14 V), and is employed for the supply of electrical energy to electrical loads such as, for example, an infotainment system. The first voltage can be designated as a HV (high) voltage, and the second voltage as a LV (low) voltage.
For the operation of the electric drive motor, the vehicle comprises an inverter, specifically a three-phase AC inverter, which is designed, from a DC (direct current) supplied by the first energy store, to generate an AC (alternating current), specifically a three-phase alternating current. The inverter comprises one or more half bridges with switching elements, specifically transistors such as, e.g. IGBTs (insulated-gate bipolar transistors), which are alternately switched.
The vehicle comprises an actuation circuit, which is designed to deliver inverter control signals for the individual switching elements of the inverter. The actuation circuit comprises driver circuits, which are designed to generate inverter control signals for the individual switching elements (specifically gate signals for IGBTs). To this end, an inverter control signal assumes a first potential (e.g. of 15 V) in order to close a switching element, and a second potential (e.g. of −7 V) in order to open the switching element. The first potential and the second potential can be generated from an intermediate circuit voltage, which typically lies between the first voltage and the second voltage (e.g. at 32 V).
In general, the actuation circuit further comprises a control unit, which is designed inter alia to ensure the transition of an on-board system of the vehicle, together with the inverter, to a safe condition (e.g. in the event of an accident situation). The control unit can also execute monitoring functions. It can thus be ensured, after the expiry of a predefined time interval (e.g. of 5 seconds), that no further voltages are present on the on-board system which exceed a predefined contact threshold (e.g. of 60 V).
The present document addresses the technical object of providing a cost-effective actuation circuit which permits a reliable transition of the on-board system to a safe condition.
The object is fulfilled by the independent claims. Advantageous forms of embodiment are described inter alia in the dependent claims.
According to one aspect, an actuation circuit is described for an inverter, specifically for a three-phase AC inverter. The inverter is designed to convert a direct current at a first voltage (specifically a HV voltage) from an electrical energy store (specifically from a HV energy store) into an alternating current (specifically into a three-phase alternating current), by means of which an electrical machine (e.g. a synchronous machine) of a vehicle is operated. Moreover, a back-up capacitor is arranged in parallel with an input of the inverter, in order to ensure that a stable input voltage is present on the input of the inverter.
The actuation circuit comprises a direct voltage converter (or DC/DC converter), which is designed to convert a direct current at a first voltage (sourced directly from the HV energy store) into a direct current at an intermediate circuit voltage (e.g. at 32 V). The actuator circuit further comprises a driver unit which is designed, on the basis of the direct current at the intermediate circuit voltage, to generate inverter control signals for switching elements of the inverter (specifically for IGBTs). The driver unit is thus supplied directly with electrical energy from the HV energy store via the direct voltage converter, thereby permitting a high degree of efficiency in the actuation circuit. Moreover, by the provision of a direct supply from the HV energy store, a galvanic isolation of the supply to the driver unit can be omitted.
The actuation circuit further comprises a discharge unit, which is supplied with direct current at the intermediate circuit voltage and is designed, in response to a discharge control signal, to switch a discharge resistor in parallel to an output of the direct voltage converter. To this end, the discharge unit can incorporate a discharge switch, which can be controlled by means of the discharge control signal and is arranged e.g. in series with the discharge resistor, in a parallel connection to the output of the direct voltage converter. By the closing of the discharge switch, the discharge resistor can be parallel-connected to the output of the direct voltage converter.
Moreover, the actuation circuit comprises a control unit (and/or monitoring unit) which is also supplied with the direct current at the intermediate circuit voltage and is designed, for the discharging of the back-up capacitor, to generate a discharge control signal, which causes the discharge unit to switch the discharge resistor in parallel to the output of the direct voltage converter. By the supply of the discharge unit and the control unit with the intermediate circuit voltage, a galvanic isolation of a data link (for the discharge control signal) between the discharge unit and the control unit can be omitted, thereby reducing the costs of the actuation circuit.
Overall, the actuation circuit permits an active discharging of the back-up capacitor via the direct voltage converter (together with the associated conversion losses) and via the discharge resistor, which is rated for the intermediate circuit voltage (together with the associated ohmic losses). This permits a reliable and cost-effective transition of the on-board system of a vehicle to a safe condition.
The control unit can be designed to determine that the transition of the back-up capacitor to a safe condition is required (e.g. in response to an instruction generated by a control device, externally to the actuation circuit). In response to the instruction, the control unit can generate the discharge control signal, thus resulting in the active discharging of the back-up capacitor. The control unit can moreover be designed, in response to the instruction, to cause the driver unit to generate inverter control signals, by means of which the windings of the electrical machine are short-circuited (thereby preventing the uncontrolled injection of electrical energy from the electrical machine into the HV intermediate circuit). To this end, e.g. the low-side switching elements of the half bridges of the inverter can be transiently switched to a closed state. The transition of the on-board system, with the back-up capacitor and the inverter, to a safe condition can thus be reliably achieved.
The back-up capacitor and the inverter are typically connected to the electrical energy store via at least one contactor. The control unit can be designed (only) to generate the discharge signal after the at least one contactor has been opened. The tapping of a discharge current from the energy store, and the associated heat-up, can thus be prevented.
The direct voltage converter can be designed to limit and/or regulate the direct current on the output of the direct voltage converter to a predefined maximum current. Reliable active discharging can thus be ensured. Specifically, an excessive heat-up of components in the on-board system of the vehicle can be prevented.
The actuation circuit can comprise one or more data interfaces with one or more components (specifically control devices) which are external to the actuation circuit. These components can be supplied by a LV on-board system (e.g. from a 12/14 V on-board system). The one or more data interfaces can be provided with a galvanic isolating device, for the purposes of protection. However, the number of data interfaces, and the quantity of electrical energy flowing therein, is typically small, such that galvanic isolation of the data interfaces can be achieved in a cost-effective manner.
The control unit can be implemented in an effective manner on a programmable integrated circuit, specifically on a complex programmable logic device, or CPLD for short.
The actuation circuit can further comprise a linear controller, which is designed to generate a supply current at a supply voltage for the control unit from the direct current at the intermediate circuit voltage. The supply voltage thereby can be e.g. 3 V or lower.
The driver unit can comprise at least one transformer circuit which is designed, from the direct current at the intermediate circuit voltage, to generate different potentials (e.g. +15 V and −7 V) for at least one inverter control signal. Electrical energy for the inverter control signals can thus be generated from the direct current at the intermediate circuit voltage by means of transformer circuits.
According to a further aspect, an on-board system is described for a vehicle which is propelled by an electrical machine. The on-board system comprises an electrical energy store (e.g. a lithium-ion accumulator), which is designed to deliver a direct current at a first voltage. The on-board system further comprises an inverter, which is designed to convert the direct current at the first voltage into an alternating current, by means of which the electrical machine is operated, and a back-up capacitor, which is arranged in parallel with one input of the inverter. The on-board system moreover comprises an actuation circuit for the inverter, as described in the present document.
According to a further aspect, a vehicle is described (specifically a road vehicle, e.g. a passenger vehicle, a heavy goods vehicle or a motorcycle), which comprises an on-board system described in the present document.
It should be observed that the devices and systems described in the present document can be employed both in isolation, and in combination with other devices and systems described in the present document. Moreover, any aspects of the devices and systems described in the present document can be mutually combined in a variety of ways. Specifically, the characteristics of the claims can be mutually combined in a variety of ways.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.